Final Words

Concluding anything about Cell requires a multifaceted look at the architecture and the platform as a whole.

First from the perspective of the game industry, more specifically Playstation 3:

Cell’s architecture is similar to the next version of Microsoft’s Xbox and upcoming PC microprocessors in that it is heavily multithreaded. The next Xbox will execute between 3 and 6 threads simultaneously, while desktop PC microprocessors will execute between 2 - 4. The problem is that while Xbox 2/360/Next and the PC will be using multiple general purpose cores, Cell relies on more specialized hardware to achieve its peak performance. Cell’s SPEs being Altivec/VMX derived is a benefit, which should mean that the ISA is more familiar to developers working on any POWER based architecture, but the approach to development on Cell vs. development on the PC will literally be on opposite ends of the spectrum, with the new Xbox somewhere in between.

The problem here is that big game development houses often develop and optimize for the least common denominator when it comes to hardware, and offer ports with minor improvements to other platforms. Given Cell’s architecture, it hardly looks like a suitable “base” platform to develop for. We’d venture to say that a game developed for and ported from the PC or Xbox Next would be under-utilizing Cell’s performance potential unless significant code re-write time was spent.

Console-only development houses, especially those with close ties to Sony, may find themselves able to harness the power of Cell much more efficiently than developers who ascribe to the write-once, port-many process of cross-platform development. Given EA’s recent acquisition and licensing-spree, this is a very valid concern.

With Cell, Sony has effectively traded hardware complexity for programmer burden, but if anyone is willing to bear the burden of a complicated architecture, it is a game developer. The problem grows in complexity once you start factoring in porting to multiple platforms in a timely manner while still attempting to achieve maximum performance.

As a potential contender in the PC market, Cell has a very tall ladder to climb before even remotely appearing on the AMD/Intel radars. The biggest strength that the x86 market has is backwards compatibility, which is the main thing that has kept alternative ISAs out of the PC business. Regardless of how much hype is drummed up around Cell, the processor is not immune to the same laws of other contenders in the x86 market - a compatible ISA is a must. And as Intel’s Justin Rattner put it, “if there are good ideas in that architecture, PC architecture is very valuable and it will move to incorporate those ideas.”

Once again, what’s most intriguing is the similarity, at a high level, of Intel’s far future multi-core designs to Cell today. The main difference is that while Intel’s Cell-like designs will be built on 32nm or smaller processes, Cell is being introduced at 90nm - meaning that Intel is envisioning many more complex cores on a single die than Cell. Intel can make that kind of migration to a Cell-like design because their microprocessors already have a very large user base. IBM, Sony and Toshiba can’t however - Cell must achieve a very large user base initially in order to be competitive down the road. Unfortunately, seeing a future for Cell far outside of Playstation 3 and Sony/Toshiba CE devices is difficult at best.

Regardless of what gaming platform you’re talking about, Cell’s ability to offer an array of cores to handle sophisticated physics and AI processing is the future. AGEIA’s announcement of the PhysX PPU (and the fact that it’s been given the “thumbs up” by Ubisoft and Epic Games) lends further credibility to Cell’s feasibility as a high performance gaming CPU.

The need for more realistic physics environments and AI in games is no illusion; the question is will Intel’s forthcoming dual and multi-core CPUs (with further optimized SIMD units) offer enough parallelism and performance for game developers, or will the PPU bring Cell-like architecture to the desktop PC well ahead of schedule? The answer to that question could very well shape the future of desktop PCs even more so than the advent of the GPU.

The only things new about Cell is its target market and being a single chip. The article mentions the TI DSP chip, but there were other similar architectures as well. One example that I'm familiar with is the MAP1310 board by CSPI. Back then, processes weren't good enough to put all the cores on a single chip but the basic architecture is the same - a PPC core to do the 'normal' stuff and two quad-core DSPs (SHARC) to do the 'work'. This board wasn't successful because it was considered too hard to program to get the performance it promised.... and this opinion is from people who live/breathe real-time systems and multiprocessing codes.

The only thing new about Cell is that a) it's all on one chip now and b) the target market is a general marketplace and not a niche.Reply

#48. OK, I was under the impression that the G5 was based on the POWER5. You're saying it's based on the POWER4 instead?

And the POWER4 and POWER5 aren't really "completely different chips" in the same way that the P4 and P3 are different chips, or in the way that the P4 and the Opteron are different chips. I can give you a list of the differences if you want. Start at http://www.elet.polimi.it/upload/sami/architetture...

The POWER5 is designed to not only be completely compatible with the POWER4 but to also to support all the optimisations from the POWER4. The only things of significance they've done is a) move the L3 cache controller on chip; b) change the various branch predictors to bimodal instead of 1-bit; c) increase the associativity and size of the caches.

"#38. You're right that the G5 is a derivative of the POWER5. The POWER5 is dual core, each core with 2way SMT giving a total of 4 'visible' cpus to the OS. The G5 is simply a single core version of the same thing."

Err no its not. POWER4 != POWER5. Hence the different names ;)

They're completely different chips.

"Well scrotemaninov I am not disputing that the POWER architecture by IBM is brilliantly done. IBM is definitely one of those companies churning out brilliant and elegant technology always in the background.

But my problem with the POWER technology is from what I understand very limitedly, is that the POWER processors in the Mac machines are a derivative of that architecture right? Why the heck are they so damn slow then?

I mean you can buy an AMD FX 55 based on the crappy legacy x86 arch and it smokes the dual 2.5 GHz Macs easily!! Is it cause of the OS? Because so far from what I have seen, if the Macs are any indication of the performance capabilities of the POWER architecture, the Cell will not be a big hit.

I did read though at www.aceshardware.com benchmark reviews of the POWER5 architecture with some insane number of cores if I recall correctly and the benchmarks were of the charts. They are definitely not what the Macs have installed in them..."

There are slow memeory systems and then theres the one used on the G5. I've heard that you can put 8 Opterons together and still get average access times across all 8 cores that are better then a single G5. Thats probably a good part of the reason the G5 was so much slower then many people thought it would be. The rest is mainly IBM's trouble making them, and their inability to ramp clock speed like they planned on.Reply

#38. You're right that the G5 is a derivative of the POWER5. The POWER5 is dual core, each core with 2way SMT giving a total of 4 'visible' cpus to the OS. The G5 is simply a single core version of the same thing.

As for the performance, Opteron is pretty much unbeatable for integer-bound applications. Itanium2 is unbeatable for FP applications. POWER5 is somewhere in the middle.

Most desktop applications are going to be integer bound. So it's not at all surprising that you find the G5 'slow' in that respect in comparison to the FX55. Plus, and this is the whole problem with the CELL, there's no point putting dual CPUs in there unless you can utilise them properly. If you have one process going flat out trying to run a heavy application and it's single threaded then you're only using about 1/4 of the CPUs you've bought for that application (for a dual G5 2.5), whereas the Opterons and FX55 stuff is more designed around quick, single threaded applications.Reply

There were moments while reading this article that I expected there to be a "Test Yourself" quiz at the end of the chapter ... er, article. Which isn't to say that articles like this are too textbookish, it's to say that they're wonderfully educational. And very, very cool for being so.

I'm half joking when I say this (but only half) -- a real "test" at the end of the article would be fun. I could see if I really understood what I read, and even get to compare my score to the rest of the, uhm, class.Reply

That's an interesting page, cuz everyone on OS X already knows that Word is slow on the Mac. It brings us back to the original statement that some ported software may be problematic performance-wise.

And the generic comment on the Mac side about Premiere is, well... use Final Cut Pro. :) Here is a test that seems a bit more useful, since it tests Cinema4D and After Effects, two apps that people use on the Mac and both of which are reasonably well optimized:

That's a good point about the memory scaling though. The IMC with AMD's chips is a definite advantage. I'm sure the G5 970MP dual-core won't get an IMC either.

Anyways, as far as this article is concerned, the G5 is kinda irrelevant. The interesting part for Apple in Cell is the PPE unit. It's also interesting that Anand says the original SPE was supposed to be VMX/Altivec. But the current SPE is not Altivec so it's less applicable for Apple, at least in the near term.

It would be interesting to know how fast a dual-core 3 GHz PPE would be in general laptop-type code, and how much power it would put out.Reply